High vacuum pump systems



Dec. 4, 1962 J. w. BEAMS HIGH VACUUM PUMP SYSTEMS 5 Sheets-Sheet 1 FiledAug. 18. 1960 INVENTOR. JESSE W. BEAMS rmaFom msSm ZQwDHEE Dec. 4, 1962J. w. BEAMS HIGH VACUUM PUMP SYSTEMS 3 Sheets-Sheet 2 Filed Aug. 18,1960 Fig.2

INVENTOR.

JESSE W. BEAMS BY v M g/ A FURNEYS Dec. 4, 1962 J. w. BEAMS HIGH VACUUMPUMP SYSTEMS 3 Sheets-Sheet 3 Filed Aug. 18, 1960 M 7 0R/VEY R 8 M m A WE B W E S B moE awo 65:35 J w e T $51.5 mw z 59. $301 United StatesPatent OfiFice 3,056,849 Patented Dec. 4, 1962 3,066,849 HIGH VACUUMPUMP SYSTEMS Jesse W. Beams, Chm'lottesville, Va., assignor to Enemplar,Inc, Washington, Ddl, a corporation of the District of Columbia FiledAug. 18, 1960, Ser. No. 50,381 Claims. (Cl. 230-417) torily, or by bothfactors.

It is a principal object of the invention to provide a pump wherein therotor is magnetically suspended in the pump chamber so that no bearingsare required, and therefore bearing lubricants are eliminated and novapor pressure therefrom is present to contaminate the pump chamber.

It is another object of the invention to provide a pump which can bebaked out without resulting damage thereto and/or subsequentlyrefrigerated, if desired, to increase its pumping efficiency.

Still a further important object of the invention is to provide animproved pumping structure resulting in improved eificiency, wherein thepumping takes place be tween the peripheral surface of a high-speedrotor and the stationary surface of a chamber whose pumping surfaces canbe further improved by providing grooves spiraling from the intake ductof the chamber toward the discharge duct thereof in the direction ofrotation of the rotor. In this type of pump, the gas molecules aredriven toward the discharge-duct portion of the surface by frictionalcontact with the rotor surfaces traveling in that direction, and thesemolecules are entrapped between the rotor and stator where the clearanceis very small, the clearance being of the order .05 centimeter or less.

Still a further object of the invention is to provide a magneticallysuspended pump rotor capable of very high rotation rates, the rate beinglimited only by the highest speed at which the rotor can be turnedwithout having it fly apart due to centrifugal forces, and the greatestspeed attainable being further increased by the magnetic suspension ofthe rotor which eliminates mechanical bearing friction. In the pumpaccording to the present invention, the surface speed of the rotor caneasily be increased to twice the average molecular speed of the gasparticles being pumped.

Another object of the invention is to provide a molecular pump suitablefor use in tandem pumping systems which also employ diffusion-typevacuum pumps and/ or rotary-type pumps. The diffusion pumps areespecially efiicient in pumping lighter molecules, whereas the presentmolecular pump is more efficient when pumping the heavier molecules, andtherefore the two types of pumps when connected in tandem tend tocomplement each other.

Other objects and advantagesof the invention will become apparent duringthe following discussion of the system;

FIG. 2 is a view, partly in cross-section showing a modified form of thepump according to the invention, the pump being located below the coilof a magnetic rotor suspension device; and

FIG. 3 is a schematic diagram showing an electronic suspension andpropulsion system suitable for use in suspending and driving the rotorsof the pumps according to the present invention.

Referring now to the drawings, FIG. 1 shows a pump comprising astationary housing including an upper plate 1, a lower plate 2, anannular wall 3 and bolt means 4 for securing the plates 1 and 2, and thewall 3, together to form a fluid-tight pump chamber generally designatedby the reference numeral 5. Within the pumping chamber '5 is located aplate 6 having a series of spiraled grooves 7 which begin at the opening7a of the plate 6 and form a continuous spiral terminating at 712 nearthe periphery of the pump chamber 5. The input to the pump chamber 5includes the inlet tube 3 extending radially through the plate 1 andterminating near the center of the annular cavity 5. This tube 8 isconnected by pipe means 9' with a region lit to be evacuated. Thedischarge from the pump chamber takes place through the tube 11 which isconnected into the outer periphery of the pump chamber 5 through thewall 3 and extends into a cold trap 12 having an outlet 12a which isconnected through suitable piping 13 with a dilfusion pump 14 andultimately with a rotary vacuum pump 15, the pumped gas dischargingthrough a pipe 16 into the atmosphere. The parts 12, 13, 14, 15 and 16are all known per se and are not considered novel in themselves. Theseparts are merely included for the purpose of illustrating one possibleuse to which the pump according to the present invention can be put.

The actual pumping is carried out by a rotor 17 made of permeablematerial and having a disc-shaped pumping portion 17a and a magneticsuspension center portion 17b. In addition, the rotor has a smalldownwardly extending conical tip 170 which lands on a bearing plate 18when the rotor is at rest. The gas pumping, however, is carried out bythe upper surface 17d of the disc, which surface lies parallel with andclosely spaced from the grooved surface of the pumping stator plate 6.

The pump housing is supported on three or more feet 19 each of whichincludes an axially adjustable screw 1% maintained at a proper elevationby a lock nut 19b, and a window 3a is supported at the end of a shorttube 312 secured in the side wall 3 of the pump housing.

The rotor 17 is suspended above the landing block 18 and is maintainedin very close, but spaced proximity to the pumping stator d by amagnetic suspension system which forms a part of the novel combinationof the present pumping system, but which is not per se novel. Thismagnetic suspension system is shown in FIG. 2 of Patent 2,733,857, whichdisclosure is substantially repeated to form a part of present MG. 3 soas to illustrate one possible means for magnetically suspending therotor 17. As stated in the objects of this invention, the importantimprovement of providing a high-speed pump having no bearings andtherefore no bearing lubricants is carried out according to the presentinvention by employing as a part of the present novel combination thismagnetic suspension system.

The magnetic suspension system comprises a solenoid 30 which whenenergized by direct current establishes a unidirectional magnetic field,the solenoid comprising approximately 28,000 turns of #22 enameledcopper wire. This number of turns provides an inductance of about 70henries with a resistance of 1200 ohms. When its core 33 of magneticmaterial is in place the total current passed through this windingshould be between and 220 milliamperes. The core 31 is of circularcross- 3 section and made of soft iron. It is suspended at its upper endon a flexible wire 32 which is attached to a stud 33 secured inadjustable position by a nut 33a. The core is located in axial alignmentwith the suspension -portion 17b of the rotor 17 and the lower end ofthe core is contained within a cylindrical vessel 34 containing arelatively heavy motor oil 35 for damping any tendency which the core 31may have to swing about the wire 32 on which it is supported. The vessel34 is made of non-magnetic material.

The windings of the solenoid 30 are supported on a disc of asbestos 36which rests upon a plate 37 located parallel with and below a brassplate 38 serving to support the upper end of the core. The plate 38 isin turn supported on studs 39 which are screwed into the upper plate 1of the pump housing.

Referring to FIG. 3, the electrical suspension circuit comprises ahigh-frequency oscillator 40 tuned to a frequency of several megacyclesby a tuned circuit 41 in the grid of the oscillator and a tuned circuit42 in the plate of the oscillator. The triode 45 comprising theoscillator has a grid circuit which includes a coil 46 forming theinductance of the tuned circuit 41. The output from the oscillator istaken from the tuned circuit 42 and is resistance-coupled with the gridof a detector tube 51. The condenser 43 is connected in series with atickler coil which is magnetically coupled with the tuned circuit 42,and serves to couple sufficient feedback to the grid circuit of theoscillator to sustain oscillations. The coil 46 can also be seen in FIG.1 located beneath the rotor 17 and has sufiicient turns thereon that itcan be tuned to the frequency of the oscillator 40 so that it can sensethe position of the rotor 17 as will be described hereinafter. Forpresent purposes, however, it is sufficient to note that the impedanceof the coil 46 is decreased or increased as the rotor moves up or downwith respect thereto and hence the tuning and output amplitude of theoscillator is dependent upon the vertical position of the rotor. It isthe purpose of the rest of the circuit to amplify variations in theoscillator amplitude so that if the rotor rises, the current in thesolenoid 30 will be decreased, and if the rotor descends the solenoidcurrent will be increased.

The oscillator 40 is coupled to the detector 55) which comprises thetube 51 connected as a cathode follower for delivering a signalproportional to the amplitude of the RF signal which is delivered to thegrid of the detector tube 51. This output signal at the lead 52, beingproportional to the amplitude of the oscillation in the oscillator 40can be used as an error signal for indicating the vertical position ofthe rotor 17. A time-derivative signal is also taken at the output lead53. The error and time-derivative signals are combined in the mixerstages 55 which includes two pentodes 56 and 57 the anodes of which areconnected in parallel and to the input of a power amplifier stage 64shown as comprising six tetrodes 61 all connected in parallel. A powersupply 63 is provided with a regulated output voltage appearing acrossthe resistance 62, and coupling is directly applied to the poweramplifier 6i) by connecting the grids of the power tubes 61 atappropriate points across the load resistor 62 which furnishes drive tothe power tubes 61. The resistor 62 is coupled with the tubes 56 and 57of the mixer and serves as a load impedance therefor. The solenoid 3%comprises the load in the plate circuits of the six power stage tubes61, and the plate voltage to these power tubes is supplied from aseparate high-voltage power supply (not shown). A voltage of about 800volts has been found suitable for this purpose.

In addition to the suspension system, FIG. 3 also shows a rotor drivesystem comprising an oscillator 70 which drives a phase shifter 71having two quadrature outputs driving power amplifiers 72 and 73,respectively. The output of one power amplifier 72 is passed through oneset of field coils 74, 75, and the output of the other power amplifier73 likewise drives another set of field coils 76, 77. All of the fieldcoils have their axes located in a common horizontal plane, and the axisof the aligned field coils 74, 75 is normal to the axis of the alignedfield coils 76, '77. These field coils provide a magnetic field in thevicinity of the rotor 17, which field has a rotating component whichrotates synchronously with the frequency of the oscillator 7t} andthereby drives the rotor as a synchronous motor armature at a rate ofrotation. dependent upon the frequency of oscillator 70. This rotationsystem is also known in the prior art and is not considered novel perse, although it forms a part of the novel combination of the presentinvention.

By reference to PEG. 1, it will be noted that the sets of drive coilsare located below the rotor, in this instance the coils '76, 77 beingvisible.

Referring now to FIG. i2, this figure shows a modified form of pumpstructure, according to the present invention, which pump structure,however, is supported by a similar magnetic suspension system and isdriven by a drive system which is also similar to that shown in FIGS. 1and 3. Like parts are therefore similarly labeled in FIGS. 1 and 2.

The pump itself as shown in FIG. 2 comprises a cylindrical housing 21closed at its upper end 21a and having tapped bores therein to receivethe rods 39 by which the magnetic suspension unit is supported. Thehousing has a bottom plate 22 which is bolted thereto to form airtightclosure of the cavity 20 of the pump. The intake duct 23 passes throughthe wall of the housing 21 and communicates with two spiral grooveswhich both pass in the same direction around the wall, the upper groovebeing labeled 21b and the lower groove being labeled 21c. The arrowsshown on these grooves are both directed from the duct 23 in the samedirection toward the upper and lower portions of the pump cavity 20,respectively labeled 20a and 20b. Grooves 21b and 210 respectivelydischarge into these end cavities 20a and 2% which are then coupled byducts 24a and 24]) which communicate with a manifold duct 24 and withthe output duct 240. Therefore, it is apparent that the gas moleculesbeing pumped enter through the duct 23, pass around the spiral grooves21b, 21c into the end cavities 20a, 20b and thence outwardly through theducts 24a, 24b, 24 and 240.

The rotor comprises an annular member 25, made for instance ofduraiumin, and attached by means of a lurality of screws 26 whichcomprise a magnetic portion 27 of the rotor. This magnetic portion ofthe rotor also includes a suspension portion 27a which is locateddirectly beneath the core 31 of the solenoid and is axially alignedtherewith. At the lower end of the rotor is a small conical tip 2511which serves as a landing means to support the weight of the rotor whenthe system is turned off and the magnetic suspension is not present.This tip 25a engages the conical surface of a small boss 22a on top ofthe closure plate 22.

Operation In operation, the rotor of the pump according to the presentinvention is suspended entirely by the flux from the solenoid 30 andcore 31 so that the pivot at the lower end of the rotor is raised off ofthe support therebelow. The flux which raises the rotor is produced by adirect current from the power amplifier 60, and as the rotor movesvertically under the attraction of the flux, its proximity to the coil46 is varied, and therefore the inductance of the coil 46 is varied soas to change the tuning of the oscillator 44. The pickup coil 46, bychanging its inductance, changes the condition of tuning of theoscillator, and therefore raises or lowers the amplitude of oscillationof the tube 45. A signal is coupled from the tune circuit 42 into thegrid of the cathode follower detector stage 51 and a DC. potentialappears across the cathode resistor 52 which is proportional to theamplitude of oscillation appearing across the tune circuit 42.

A portion of the potential is taken off of the resistance 52 and passedthrough a battery which serves to reduce the DC. level thereof withoutdecreasing the amplitude of signal variations. These signal variationsare a direct error signal proportional to the vertical position of therotor and are connected to one input of a mixer circuit 55, comprisingpentodes 56 and 57 having their plates connected in parallel.

In addition, an RC dilferentiating circuit is connected across thecathode resistor 52a which gives a signal at the lead 53 which isproportional to the time-rate-of-change of rotor height. This derivativesignal when mixed with the error signal provides a component whicheffectively damps any up and down motion of the rotor.

The error and derivative signals are separately amplified in the tubes56 and 57 and mixed in their plate circuits and applied to the grids ofsix beam power pentodes 61 which regulate the current through thesolenoid 30 While passing it through the milliammeter A so that anindication is present of the average current value. The magnitudes ofthe error signal and of the derivative signal can be individuallyadjusted and the mixed component thereof controls the current to thesolenoid 30 in such a way that when the rotor approaches the coil 46 inFIG. 1, the amount of current in the winding 30 of the solenoid isincreased and when the rotor rises higher above the coil 46, the amountof current in the solenoid is decreased, and by proper adjustment anequilibrium can be had at which the rotor is suspended freely in space.Note that in FIG. 2 since the coil 46 is above the rotor 27 rather thanbelow it, a different adjustment of the tune circuit 41 on the otherside of resonance is necessary to provide the opposite operation fromthat just described above.

The horizontal position of the rotor is determined by the symmetricalmagnetic field at the bottom of the core 31. The rotor automaticallyseeks the strongest part of the electric field, which is at the centerof the pole 31 and at the center of the rotor, but it is desirable toprovide horizontal damping in order to prevent eccentric oscillationsabout the axis of rotation if the rotor is displaced in a horizonaldirection. For this purpose, the cylindrical core 31 comprising the poleis hung on a wire 32 so that the core is supported like a pendulum, andthe bottom end of the core is immersed in a dash-pot 34 of oil 35. Themass and size of the rotor are so related to the dimensions and weightof the core that the core follows any eccentric motions of the rotorfrom the center position. However, the motion of the core 31 is dampedby the oil 35 in the horizontal direction and therefore the oscillationsof the rotor are also damped by the oil 35. When properly adjusted, nomovement, either horizontal or vertical, can be observed in theequilibrium position of the rotor.

With the rotor thus suspended, the oscillator 70 provides the energy ofrotation by passing quadrature currents through the two sets of windings75, 74 and 76, 77 of the field. As stated above, since quadraturecurrents are applied to these field windings, the rotor automaticallylocks into step with the rotating field of these windings and operatesin the same way as the armature of a synchronous motor.

Thus it will be seen that I have provided an improved combination ofelements which can pump gas molecules to achieve a very much increasedvacuum without contamination of the evacuated region by vapor from suchlubricants as have heretofore been necessary to lubricate the bearingsof prior art pumps. Moreover, it will be observed that there is nothingin the pump body per se, in-

cluding the rotor, the stator, and the pump housing, which can not bebaked out at relatively high temperatures, such as 400 degrees F. forlong periods of time, i.e. several hours or so. This baking out isextremely important, and can be sufliciently done only where nolubricant is required in the pump, since the lubricant tends to vaporizeat the elevated bake-out temperatures.

I do not limit my invention to the precise forms illustrated in thedrawings, for obviously changes may be made therein within the scope ofthe appended claims.

lclaim:

l. A molecular gas pump comprising a housing having a cavity; inlet andoutlet duct means communicating with said cavity; a stator surface inthe cavity, a rotor in the cavity having an annular portion of magneticmaterial disposed along the axis of the rotor and having a rotor pumpingsurface substantially coextensive with said stator surface and locatedin closely spaced proximity thereto; magnetic suspension means locatedoutside of said housing and coacting with said magnetic material forsuspending the rotor freely in space within the cavity; androtating-field generating means located outside of said housing andmagnetically coupled with said annular portion of magnetic material forimparting rotation to the rotor.

2. In a pump as set forth in claim 1, the housing having an openingtherein; a transparent window in said opening; and means to seal thewindow therein.

3. A molecular gas pump comprising a housing having a cavity; inlet andoutlet duct means communicating with said cavity; a stator surface inthe cavity; a rotor in the cavity having a rotor pumping surfacesubstantially coextensive with said stator surface and symmetricallydisposed about its axis of rotation; magnetic means located outside thehousing and coacting with the rotor for suspending the rotor free of allcontact with other elements of the pump for rotation about said axis;rotorposition sensor means adjacent the rotor and controlling saidmagnetic means for maintaining the rotor pumping surface located inclose proximity to said stator surface, the gas molecules passingbetween said surfaces in transit from the inlet duct means to the outletduct means; and drive means located outside of the housing and coactin'gwith the rotor for imparting rotation to the rotor.

4. In a pump as set forth in claim 3, the housing having an openingtherein; a transparent window in said opening; and means to seal thewindow therein.

5. In a vacuum pumping system, the combination of a pump having ahousing including a cavity connected with a region to be evacuated and adischarge duct lead ing out from said cavity, and the pump includingrotor means located within said chamber for impelling gas moleculestoward said discharge duct and the rotor means having an axiallydisposed portion of magnetic material; magnetic suspension means locatedoutside of and separable from said pump for coacting with and suspendingthe rotor freely in space within said cavity; and rotating fieldgenerating means located outside of the pump and magnetically coupledwith said portion of magnetic material for imparting rotation to therotor.

References Cited in the file of this patent UNITED STATES PATENTS1,257,288 Kirby Feb. 19, 1918 1,492,846 Holweck May 6, 1924 2,191,345Gaede Feb. 20, 1940 2,733,857 Beams Feb. 7, 1956 2,747,944 Baermann May29, 1956

